This invention pertains to mechanical pipe couplings, the ends of which swivel relative to one another even under extremely high fluid pressure. These type couplings find primary utility in oil well drilling and service operations, such as the pumping of drilling mud, fracturing, and squeeze cementing.
In the typical oil well drilling operation, there is a seemingly endless need to string pipe lines to move the various fluids used and encountered during drilling and service. These lines are moved and modified often. Further, the terrain over which these lines must run will often be uneven. Accordingly, it is virtually impossible to make the required connections using the standard straight pipe and connectors. Rather, swivel couplings are an absolute necessity, as they provide the flexibility required for rapid laying and dismantling of pipelines. The prior art is, therefore replete with swivel couplings of various designs.
As the pipe typically encountered at the oil well is large, usually two to four inches in diameter, and because the pipe sections are typically moved and installed by manual labor, it is important that the swivel couplings be as light-weight as possible, without sacrificing the strength or flexibility required by the job. Further, because a great number of these swivel couplings will be utilized at each well site, expense is also an important consideration. Accordingly, a design goal is to simplify the swivel coupling for ease of manufacture, as this permits lower cost. Most importantly, however, the swivel couplings must be strong--able to withstand not only the extremely high fluid pressures, but also the pulsating action and rough handling to which they are routinely subjected. These multiple goals, inherently divergent, are difficult to obtain. Indeed, the prior art swivel coupling designs have suffered from one or more of the drawbacks of heavy weight, high expense or poor performance.